The narrator is Greg who is obviously writing the book (more than once he questions whether the reader will make it to the end of 'this stupid book'). Throughout the story, Greg is self deprecating to the reader and the other people in his life.
His goal throughout his school life it so go unrecognized. He has been successful at this by carefully navigating the different cliques. He makes himself acquainted with each one without becoming involved with them. This fragile network he has created is imperil when a girl he dated a long time ago (and treated badly during the break up) is diagnosed with cancer. Only the unrelenting urging of his mother could make him contact the girl, Rachel, to be her friend in her time of need. His senior year is turning out much differently than he planned.
And then there's Earl. Greg and Earl seemingly have little in common except for the movies they make together. They have been making them for years and admit they are not very good. Bad acting, terribly lighting, cheap costumes, homemade props all lead to a series of films no one else would want to see, and that is just fine because Earl and Greg both agree to never share them with anyone.
In addition to the typical format for a book, Greg often uses lists and a script format (to recreate dialogue). He deals with his own self esteem issues with humor that sometime works and sometimes gets him into trouble. Although Greg might not agree, he has an interesting life filled with intriguing characters.